AudioTools's Spectrum Analyzer component uses FFT on batches of samples recorded at the microphone. Hann windowing reduces aliasing. Recorded spectra may be stored as files on the SD card, and then loaded later and displayed together with the live spectrum.

(The "Store" button will store the current live spectrum with a filename of your choice. The "Load" button brings up a list of stored spectra. One of these can be chosen, or the "Cancel" item selected to return to the main display, or the "Clear" item selected to remove the currently loaded spectrum.)

Data collection can be paused and restarted.

The deciBel meter component uses IIR filters and exponential averaging to calculate Flat, A and C weighted response at speeds of Fast, Medium and Slow.

RT60 measurements can be made by starting the RT60 component and using a loud clap (or similar) to trigger the measurement. RT60 times measure how much reverberation or echo there is in a room or auditorium.

Wave frequency is set using the arrow buttons or directly via the keyboard. The upper display shows the sound picked up by the microphone in real time. This can be useful for evaluating the response to an audio system being fed with the generated sound. Better results can be obtained by using a headset adapter/splitter that allows an electrical signal to be sent from the device to the audio system.

The Impulse signal is a delta issued approximately once per second. Impulses can be used to measure the frequency response of audio systems: they have a flat frequency distribution.

The accuracy in frequency of the generated periodic signals is quite good: on the Motorola Droid, errors were of the order of 1% throughout most of the range. Sine wave fidelity is good throughout most of the audio range. Other signals' leading and trailing edges show ringing and decreasing frequency response artifacts in the upper ranges.

Reviews

(July 2011) A review from Sound & Vision magazine. "With Audio Tool on your Droid, you always have a full-featured
acoustical analysis tool right in your pocket for just a few bucks. It’s
the best option I’ve ever seen for DIY audio testing."

Wave frequency is set using the arrow buttons or directly via the keyboard. The upper display shows the sound picked up by the microphone in real time. This can be useful for evaluating the response to an audio system being fed with the generated sound. Better results can be obtained by using a headset adapter/splitter that allows an electrical signal to be sent from the device to the audio system. A suitable device is shown at the bottom of this page.

The Impulse signal is a delta issued approximately once per second. Impulses can be used to measure the frequency response of audio systems: they have a flat frequency distribution. For frequency response measurements, the SPLMeter Android application (below) can be used.

The accuracy in frequency of the generated periodic signals is quite good: on the Motorola Droid, errors were of the order of 1% throughout most of the range. Sine wave fidelity is good throughout most of the audio range. Other signals' leading and trailing edges show ringing and decreasing frequency response artefacts in the upper ranges.

SPLMeter for Android

V2.3 adds ISO 1/3 octave levels display

SPLMeter monitors sound picked up by the mic on your Android device and converts it to an SPL in deciBels, as well as showing its frequency composition as a spectrum. The meter has three speeds: Fast, Medium and Slow. Peak spectrum can be shown as well as the detected frequency of maximum strength, in Hz.

Operation Details

Input audio data from the microphone is read out as 16 bit PCM samples at a sample rate of 22,050 samples per second. This sets the maximum detectable SPL level to 90dB (equivalent to 20log(65536)), and the maximum detectable frequency to around 10kHz.

A calibration adjustment is made internally that matches the dB SPL shown by SPLMeter to that measured by the Ivie Technologies IE35 professional grade meter. Metering uses an exponential filter whose speed can be adjusted to Slow, Medium or Fast using a button on screen.

The PCM samples are sent to a FFT in batches of 2048 ... this fixes the lowest detectable frequency to around 10Hz. The frequuency spectrum is plotted on a Hz log scale in the standard way, with dB levels shown on the vertical axis for each point.

The frequency at which the maximum value of SPL is detected is shown on the display, and its position indicated with a small downwards pointing arrow.

The application also shows the real time audio PCM signals as they are collected from the Mic via the Android device's audio subsystem. These are plotted on the lower display from left to right, as a function of time. This display auto scales as a function of the maximum detected signal level.

Buttons are provided that allow the display to be paused and to show or hide the peak measured spectrum.

If the mic signals clip due to overload (very loud noise) then the Mic sample display background changes to red.

Processing Speed

The number shown immediately after the "Mic" legend indicates the frame
rate of the application, in milliseconds - in other words the time for data collection and processing ... ideally, at the chosen sample
rate, this should be around 200ms, but will vary depending on the speed
of the Android device's processor and whether other applications are
taking shares of the CPU. On the Motorola Droid it runs at around 250ms, on the HTC G1 it is slower, around 800ms.

OBDPlot

This is a tool for monitoring the Motronic ECU in e.g. the Porsche 911 model 964. Please see the dedicated page on OBDPlot for more details (including source code).

AudioCaps

Prints a list of the supported recording and playback formats on your Android device.

v1.4 actually confirms play/record capability by send/receive of samples to the audio hardware
v1.3 unreleased version
v1.2 refinement to rate test
v1.1 makes more rigorous check of record rate support

Ghostroid - Paranormal Activity Detector

The Ghostroid application uses the microphone in your Android device to measure ambient subsonic, sonic and
supersonic sound in your environment. Using this information it
calculates a ParaNormalQuotient (PNQ) which is a measure of potential
paranormal activity in the vicinity.

Theory of Operation

It has been
reported that paranormal activity is evidenced by sounds inaudible, or
barely audible, to the human ear. Animals, whose hearing is more acute at
higher frequencies than ours, are able to detect supersonic sounds,
generally above 12-15 kiloHertz or so. For example, dogs are reported to
behave oddly during supernatural events. Sounds of very low frequency,
less than a hundred Hertz or so, are normally felt rather than heard by humans. The built-in microphone circuitry in most handheld devices is designed to detect frequencies in the audio range,
but there is some residual response from the circuitry at the very low
(subsonic) and very high (supersonic) frequencies.

Ghostroid uses fast
software-based Infinite Impulse Response (IIR) filters to measure the
level of sub- and super-sonic sound pressure waves arriving at the
microphone. It also measures the audible sound level. The three ranges
are shown on the Ghostroid display via three meters, which
move dynamically and are updated several times a second. The Para Normal
Quotient (PNQ) is calculated from a formula that sums the sound levels in
the sub- and super- sonic ranges, and subtracts the audible range value.
This yields a number which increases as the sub- and super- frequencies
(which are difficult or impossible for us to hear) increase, as compared
to the audible frequencies.

The PNQ value is shown by a set of
concentric bands at the centre of the display. High PNQ
values may be caused by a variety of events: Low frequency rumbling
(e.g. from heavy trucks or machinery), High frequency noises (e.g. dog
whistles, or keys jangling) as well as Supernatural phenomena (please don't drop your Android when you run away in fright!)

V1.3 adds the Magnetic Field gauge. This measures the absolute value of the magnetic field near the Android device, using the built in magnetometer.

Ghostroid is a port to Android of the well-established "Pocket Ghost" application for Windows Mobile. Although I remain sceptical about the existence of paranormal activity, and the effectiveness of this application to detect it, I have received several reports over the years of Pocket Ghost being successfully used by paranormal investigators. Here are a couple of quotes:

1) "I have used the pocket ghost program on my I-mate Jasjam and in all cases the Sub-sonic and Super-sonic reading peaked

at 85 to 90 and did not drop down until the visions (or what ever they were) had gone."

2) "I have seen your program successfully used by a professional parapsychologist during an investigation in London."

3) "I am a member of several paranormal groups and investigate the most paranormally active sites within the U.K.

On one such investigation a parapsychologist was using your 'Pocket Ghost' to great effect."

Randomness

Randomness flips a coin, rolls a pair of dice, or selects a random Web page for you from the millions available. It's all very random. Suggestions for further randomness e.g. lottery numbers, are welcomed.

V1.5 Initial random version number

Sensors

V2.2: Add zoom in/out buttons and Mag Field on/off button for Monica

Simple application showing the output from the 3-axis accelerometer and magnetometer. Scales variable between 0.01 and 20g for acceleration.

Metaloid

Uses the built in magnetometer to show the magnetic field near the Android. Three metering speeds: Fast, Medium, Slow plus Zero offsets, two scales.

Use as a metal detector: pass the Android over a ferrous metal object and observe the needle behaviour.

Accuracy determined by phone hardware.

v2.1 Cosmetics & ad supported

Handheld Audio Spectrum Analyzer (HASA)

HASA is a handheld audio frequency spectrum analyzer for Windows Mobile devices. Frequency components of sounds picked up by the built-in microphone are shown in real-time. HASA is supplied with full instructions for use.